Improvement of ductility in Ti-6Al-4V alloy via laminated structure by additive manufacturing

Abstract

Titanium alloys are widely applied for fields including aerospace, automotive, and biomedical industries due to their superior properties including high strength-to-weight ratio, corrosion resistance, and biocompatibility. However, further improvement of mechanical properties by implication of sophisticated shape is limited, due to their poor machinability. Additive manufacturing (AM) is one of the powerful solutions to this problem, which has been rapidly emerged these days. However, additively manufactured product shows anisotropic microstructure and mechanical properties due to a severe thermal gradient. For example, Ti-6Al-4V alloy by AM process shows general fracture elongation in building direction, while it shows very low fracture elongation in a transverse direction which is perpendicular to the building direction. In this study, the fracture elongation in AM process was improved by a laminated structure which is consisted of a Ti-6Al-4V layer and pure titanium layer. The pure titanium layer performs a role in the relief of columnar microstructure of prior β grains, and also stress partitioning about the Ti-6Al-4V layer. These two factors lead to an increase in elongation in the transverse direction. Also, continuous composition and microstructure prevent stress from concentrating at the layer interface, which leads to relatively high elongation in the building direction of the laminated structure. This study is significant in respect of showing the possibility of designing hetero-microstructure (in here, laminated structure) through AM process to cover its fundamental limitation. So, other follow-up studies will be conducted to increase the other mechanical properties, especially the strength, not only relief of elongation.